The present invention relates in general to control valve systems for operating multiple actuators, and, more specifically, to interconnecting control valves for separate actuators such that a fault in one control valve quickly results in deactuation of the other control valve.
The operation of fluid power controlled machinery, such as a mechanical power press, can damage a press or cause an unsafe condition if not properly controlled. In order to comply with engineering standards, governmental regulations, and good practice, a double valve is typically used as a control element for such machinery so that upon an operational malfunction, such as a valve failure, a press repeat, or overrun cycle due to a single malfunction of a valve, damage to the press or unsafe conditions can be avoided. The use of a double valve also provides the advantage of automatic lockout of valve operation during an operational malfunction to prevent further machine cycling until the malfunction can be corrected and the valve reset. Examples of double valves satisfying the forgoing requirements are shown in U.S. Pat. Nos. 6,840,258 and 6,840,259, both assigned to Ross Operating Valve Company and both incorporated herein by reference.
Large presses typically have separate clutches and brakes for controlling their operation. A double valve controlling the brake actuator is actuated in order to supply fluid power pressure to disengage the brake. A second double valve controlling the clutch actuator is actuated to engage the clutch so that motive power is applied to the press. The timing of the actuation and deactuation of the clutch and brake must be accurately controlled in order to avoid damage to the press. For example, a failure in the brake double valve causing the brake actuator to release so that the brake is applied at the same time that the clutch actuator is still engaged could result in attempting to cycle the press while the brake is engaged. Attempting to cycle the press while the brake is engaged can cause an unsafe condition or damage the actuators or the press. Therefore, when one of the double valves becomes faulted, the other valve must be quickly deactuated so that such a simultaneous actuation is avoided.
Conventional techniques for addressing the potential problem of continued operation of one double valve when the other valve is faulted have been subject to various disadvantages which have resulted in them being unacceptable under the relevant standards. Examples of prior art methods include the use of flow control valves connected between each double valve and its respective actuator, quick dump valves connected to the clutch actuator for timing, or pressure switches used to indicate a valve fault and to cause a second valve to deactuate.
Another prior art approach has been to slow the actuation time of the clutch control valve by restricting the inlet supply to the pilots. Simultaneously, deactuation time of the brake valve has been slowed by restricting the exhaust ports of the pilots. This arrangement prevents overlap of the clutch and brake during normal operation, but does not monitor the system for valve faults. Therefore, additional components need to be used to monitor the system and to deactuate both valves whenever either valve enters a fault state. A similar method to prevent overlap of the clutch and brake operation has been to restrict airflow to the main inlet of the clutch control valve and to restrict the main exhaust of the brake control valve. This alternative method similarly requires additional components for monitoring and deactuating both valves whenever either valve becomes faulted.